# CVE-2026-97985: af_unix: Update last skb marker in manage_oob().

> A local attacker can cause a CPU busy-wait denial of service in the Linux kernel by triggering a specific out-of-band socket condition during a blocking peek operation.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 25 Sep 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-104352, BELL-CVE-2026-97985, DEBIAN-CVE-2026-97985, GHSA-cq66-2f6w-rhg5, UBUNTU-CVE-2026-97985

## What is CVE-2026-97985?

CVE-2026-97985 is a denial of service vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

af_unix: Update last skb marker in manage_oob().

Fahad Alharbi reported that blocking recv(MSG_PEEK) could hog CPU
due to OOB skb.

In the following cases, manage_oob() skips OOB skb(s) and returns
NULL for the last recv(MSG_PEEK):

  socketpair(AF_UNIX, SOCK_STREAM, 0, sk);

  1) skb -> OOB skb -> NULL
     send(sk[0], "ab", 2, MSG_OOB);
     recv(sk[1], buf, 0, MSG_PEEK);

  2) skb -> consumed OOB skb -> NULL
     send(sk[0], "ab", 2, MSG_OOB);
     recv(sk[1], buf, 1, MSG_OOB);
     recv(sk[1], buf, 0, MSG_PEEK);

  3) consumed OOB skb -> OOB skb -> NULL
     send(sk[0], "a", 1, MSG_OOB);
     recv(sk[1], buf, 0, MSG_OOB);
     send(sk[0], "b", 1, MSG_OOB);
     recv(sk[1], buf, 1, MSG_PEEK);

Then, @copied is 0 in unix_stream_read_generic() (zero-length buffer,
or non-OOB skb is not yet consumed), and unix_stream_data_wait() is
called.

However, it returns immediately because @last is not updated in
unix_stream_read_generic(), and the thread busy-waits for a new skb.

Let's update @last in manage_oob().

For MSG_PEEK, @last is updated with the skipped OOB, and for the
non-peek case, @last matches the returned value (when !copied)
because OOB is unlinked.

Note that manage_oob() is inlined and no stack canary is added.

## Which versions are affected by CVE-2026-97985?


## How do I fix CVE-2026-97985?

Apply the vendor's patch.

## Is CVE-2026-97985 being exploited?

There is no known exploitation of CVE-2026-97985 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-97985 and fix it if it is affected.

What it is: CVE-2026-97985 is a denial of service vulnerability in Linux, published on 25 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-97985 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-97985/ (Markdown: https://insights.sbomify.com/CVE-2026-97985/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-97985
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-97985
- OSV: https://osv.dev/vulnerability/CVE-2026-97985

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-97985/
Summaries are generated and may contain mistakes; the official description above is the record.